A flat-panel device contains a pair of generally flat plates connected together through an intermediate mechanism. The two plates are typically rectangular in shape. The thickness of the relatively flat-structure formed with the two plates and the intermediate connecting mechanism is small compared to the diagonal length of either plate.
When used for displaying information, a flat-panel device is typically referred to as a flat-panel display. The two plates in a flat-panel display are commonly termed the faceplate (or frontplate) and the baseplate (or backplate). The faceplate, which provides the viewing surface for the information, is part of a faceplate structure containing one or more layers formed over the faceplate. The baseplate is similarly part of a baseplate structure containing one or more layers formed over the baseplate. The faceplate structure and the baseplate structure are sealed together, typically through an outer wall, to form a sealed enclosure.
A flat-panel display utilizes mechanisms such as cathode rays (electrons), plasmas, and liquid crystals to display information on the faceplate. Flat-panel displays that employ these three mechanisms are generally referred to as cathode-ray tube ("CRT") displays, plasma displays, and liquid-crystal displays. The constituency and arrangement of the display's faceplate structure and baseplate structure depend on the type of mechanism utilized to display information on the faceplate.
In a flat-panel CRT display, electron-emissive elements are typically provided over the interior surface of the baseplate. The electron-emissive elements are arranged in a matrix of rows and columns of picture elements (pixels). Each pixel typically contains a large number of individual electron-emissive elements. When the electron-emissive elements are appropriately excited, they emit electrons that strike phosphors arranged in corresponding pixels situated over the interior surface of the faceplate.
The faceplate in a flat-panel CRT display consists of a transparent material such as glass. Upon being struck by electrons emitted from the electron-emissive elements, the phosphors situated over the interior surface of the faceplate emit light visible on the exterior surface of the faceplate. By appropriately controlling the electron flow from the baseplate structure to the faceplate structure, a suitable image is displayed on the faceplate.
The electron-emissive elements in a flat-panel CRT display typically emit electrons according to a field-emission (cold emission) technique or a thermionic emission technique. In either case, but especially for the field-emission technique, electron emission needs to occur in a highly evacuated environment for the CRT display to operate properly and to avoid rapid degradation in performance. The enclosure formed by the faceplate structure, the baseplate structure, and the outer wall is thus fabricated in such a manner as to be at a high vacuum, typically a pressure of 10.sup.-7 torr or less for a flat-panel CRT display of the field-emission type. One or more spacers are commonly situated between the faceplate structure and the baseplate structure to prevent outside forces, such as air pressure, from collapsing the display.
Any degradation of the vacuum can lead to various problems such as non-uniform brightness of the display caused by contaminant gases that degrade the electron-emissive elements. The contaminant gases can, for example, come from the phosphors. Degradation of the electron-emissive elements also reduces the working life of the display. It is thus critical to hermetically seal a flat-panel CRT display.
A flat-panel CRT display of the field-emission type, often referred to as a field-emission display ("FED"), is conventionally sealed in air and then evacuated through pump-out tubulation provided on the display. FIGS. 1a-1d (collectively "FIG. 1") illustrate one such conventional procedure for sealing an FED consisting of a baseplate structure 10, a faceplate structure 12, an outer wall 14, and multiple spacer walls 16.
At the point shown in FIG. 1a, spacer walls 16 are mounted on the interior surface of faceplate structure 12, and outer wall 14 is connected to the interior surface of faceplate structure 12 through frit (sealing glass) 18 provided along the faceplate edge of outer wall 14. Frit 20 is situated along the baseplate edge of outer wall 14. A tube 22 is sealed to the exterior surface of baseplate structure 10 through frit 24 at an opening 26 in baseplate structure 10. A getter 28 for collecting contaminant gases is typically provided along the inside of tube 22. The structure formed with baseplate structure 12, outer wall 14, and spacer 16 is physically separate from the structure formed with baseplate structure 10, tube 22, and getter 28 prior to sealing the display.
Structures 12/14/16 and 10/22/28 are placed in an alignment fixture 30, aligned to each other, and brought into physical contact along frit 20 as shown in FIG. 1b. Alignment fixture 30 is located in, or is placed in, an oven 32. After being aligned and brought into contact, structures 12/14/16 and 10/22/28 are slowly heated to a sealing temperature ranging from 450.degree. C. to greater than 600.degree. C. Frit 20 melts, sealing structure 12/14/16 to structure 10/22/28. The sealed FED is slowly cooled down to room temperature. The heating/sealing/cool-down process typically takes 1 hr.
After having been sealed, the FED is removed from alignment fixture 30 and oven 32, and is placed in another oven 34. See FIG. 1c. A vacuum pumping system 36 is connected to tube 22. With a heating element 38 placed around tube 22, the FED is pumped down to a high vacuum level through tube 22. The FED is then brought slowly up to a high temperature and baked for several hours to remove contaminant gases from the material of the FED. When a suitable low pressure can be maintained in the FED at the elevated temperature, the FED is cooled to room temperature, and tube 22 is heated through heating element 38 until tube 22 closes to seal the FED at a high vacuum. The FED is then removed from oven 34 and disconnected from vacuum pump 36. FIG. 1d shows the sealed FED.
The sealing process of FIG. 1 is unsatisfactory for a number of reasons. Even though multiple FEDs can be sealed at the same time, the sealing procedure often takes too long to meet commercial needs. In addition, the entire FED is heated to a high temperature for a long period. This creates concerns relating to alignment tolerances and can degrade certain of the materials in the FED, sometimes leading to cracking. Furthermore, tube 22 protrudes out of the FED. Consequently, the FED must be handled very carefully to avoid breaking tube 22 and destroying the FED. It would be extremely beneficial to have a technique for sealing a flat-panel device, especially a flat-panel display of the field-emission CRT type, that overcomes the foregoing problems and eliminates the need for pump-out tubulation such as tube 22.